I also can’t stand restrictive sleeping bags.
I’ve got a Snugpak Softie Autumn Chrysalis (3 season). The sleeping bags in this range are great as they have a baffle zip that can be used to give you extra room. This is the only bag I’ve used so far that I feel comfortable zipping up, I used to just use sleeping bags like a duvet and never actually get into them 🙂
Are you planning on using it somewhere real cold (i.e. not in UK)?
If not, I wouldn’t bother with anything more than a 3 season. i’ve used my snugpak in scottish winter conditions – it’s comfy down to -10, plus you can then ‘add’ additional warmth by wearing extra layers, using a silk liner or sleeping in a tent 🙂
Is that Exped sleeveless? If so it doesn’t seem like it would make a good 4/5 season bag (cold arms!).
Another similar concept is the german army sleeping bag. Not sure if you can get this with different temp ratings…
Nick